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Multistage Power Amplification Storage Systems for Dedicated Photovoltaïc Applications and Harvesting
Alfred Rufer, Simon Delalay
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Intermediate and Final Energy Use

Abstract

The paper discusses the principle of power amplification, as it can be found in many systems powered by PV panels and buffered by batteries. Under different categories of application examples one is given by compacting containers for plastic or other waste materials. The main goal of such systems is to supply high-power intermittent systems from low power sources. The studied example discusses an energy harvesting system using a low power solar PV collection system that is dedicated to power a specific application, sequentially operated at high power. The transformation of the power level is achieved using intermediary storage, where the charging sequence is characterized by a very low power level for longer time, followed by a shorter discharge sequence of the storage means with a much higher instantaneous power. The performance of the PV harvesting system is discussed from the point of view of its energy efficiency. Several solutions are discussed, and finally, a new 2-stage harvesting system is introduced. The requirement of a multistage amplification system is related to the power amplification ratio itself. The design method for the system relies on the concept of the so-called “Modified Ragone Representation”, MRR, that is shortly introduced in the paper. A prototype realization of the two-stage system is also presented.

Introduction

Energy storage devices or accumulators are often inserted to enable a system to cope with extremes of demand using a less powerful source, to respond more quickly to a temporary demand, or to smooth out pulsations. More recently, new applications of solar powered devices are appearing, allowing many tasks that need short-term high-power demand, while being powered by small photovoltaic cells. Collecting solar power with PV panels with a relatively high efficiency is enabled by following strict conditions related to the maximum solar irradiation and to the conversion efficiency of the PV cells. Usually, PV installations have the property of consuming a large surface for a defined power level in the order of magnitude of 10 m2 for 1 kWp. Specific applications such as compacting waste collectors or other applications as the composter machine are characterized by the small surface of their PV collectors and through the higher instantaneous power needed by the internal actuator. Because of the typical intermittency of solar irradiation, but also in order to provide a given level of power to the final application, this kind of systems usually need embed energy storage components such as batteries. High power density is generally required in order to achieve good energy efficiency.

One can assume that usually, the power density of an accumulator during the charge process is identical to its discharge power density. In the presented application framework, the real operation conditions are different. Indeed, even if the averaged power required is relatively low, the impulse power peak can be several orders of magnitude higher than the latter. In such a case, an energy harvesting system with very low input power level can be designed. This paper will introduce the design criteria of such harvesting systems that are able to provide a high power level to the final application, with the help of an energy storage element. During the discharge of that accumulator, a high power density must be available in order to keep the energy efficiency at a good level.

The principle of Power Amplification

A given amount of energy can be represented by the time integral of an instantaneous value of power, leading to the representation by a geometric surface. The simplified model of figure 2 represents the corresponding energy amount under the curve of a given power level. In this representation, the power P1 is kept constant during the time duration t1. At the right side of the figure, the higher power level P2 is also kept constant during the shorter time duration t2.

In the idealized case where the energy amount would be kept constant in the transformation from P1*t1 to P2*t2, the energy efficiency is defined as unity. The power amplification factor PAF is defined as the ratio of P2/P1. In the non-ideal case, the energy efficiency is defined as P2*t2 / P1*t1

For both the charge and discharge process of an energy storage device, the energy efficiency can be calculated. Its dependency from the actual value of the exchange power level has been highlighted in [1] and [2].

2.1 The Modified Ragone Representation MRR

Figure 3 is one general representation that illustrates the energy losses of one storage device, where both effects of first the self-discharge loss and second the load-related loss caused by the internal series resistor of an ideal battery are represented. Figure 3a shows the equivalent scheme of an ideal battery, where an ideal voltage source (U0) is represented, together with the parallel resistor Rp and the series resistor Rs. The amount of stored energy is represented through the quantity W0.

Figure 3b shows the so called Modified Ragone Representation MRR [3], indicating the amount of energy to be extracted from a storage device while being discharged from a full state of charge down to zero. The red curve illustrates the properties of an energy-type accumulator, the blue curve is related to a power-type accumulator.

The diagram represents the energy amount that one can recover from an ideal storage device taking into account the self-discharge (Rp in Figure 3a), and also the internal loss in the series resistor Rs. The horizontal scale of Fig. 3b represents the power at what the energy is recovered. The scale is chosen as a logarithmic scale in order to represent as well the extreme low power values, as the high solicitations. The left side of these diagrams illustrate the domain where the power level for the discharge is in the range of the self-discharge power. The extracted energy amount is near zero. On the right side of the diagrams, the operation conditions are that the internal losses due to the presence of the series resistor are strongly reducing the amount of extractable energy.

In the middle of the curves, the normal operation domain is represented where an acceptable amount of energy can be extracted over about 2 or 3 decades of the power range.

For the charging process, similar curves can be defined, because the self-discharge as well as the internal series losses are modelled through the same equivalent scheme.

As a consequence, one can recommend to charge and discharge a storage device at a power level situated between the positive and negative slope of the MRR curve, preferably at power levels where the curve reaches sufficient high values.

Energy harvesting with small photovoltaic panels and a two stage amplification

An energy harvesting system is developed with the goal to provide energy to a specific application characterized by an intermittent operation. The harvesting of the energy amount is done from a minimal surface of PV panels. A cascaded energy conversion and storage system overtakes the function of the power transformation.

The efficiency of the 1st stage power amplification with supercapacitors

As explained at the beginning of this paper, the first stage of the power amplification is achieved using direct coupled supercapacitors. Figure 6 highlights the operation principle of the so called « riding cap » , where the power delivered by the PV panels PPV is drawn on the left side of the figure as a function of the panels voltage VPV. The corresponding value of the voltage of the PV panels that is identical to the voltage of the direct connected supercapacitors is represented as a time-function in the upper right part of the figure.

The instantaneous power, fed to and delivered by the supercapacitors is represented in the lower curve of figure 6. Pin is the value of the charging power level of the supercapacitors, and Pout is their discharging value. The charging and discharging durations are indicated as tin and tout. In the following calculation of the energy efficiency of this first power amplification stage, the variation of the value of the supercapacitor’s voltge is neglected, due to the fact that the hysteresis of the sliding-mode controller is kept small. The calculation is done with a constant parameter USC corresponding to the mean value.

The calculation of the energy efficiency of the power amplification is based on an equivalent scheme . A simplified calculation is given here, where not only the voltage variations of the supercapacitors is neglected, but where the charging/discharging current is kept constant. A more accurate calculation of this efficiency can be found in [3].

The Modified Ragone Representation (MRR) for the evaluation of the efficiency of a two stage amplification system

The method of the Modified Ragone Representation has been presented in section 2.1 for a one-stage storage system. The two stage system represented in figure 4 can be analyzed through the same tool of the Modified Ragone Representation. The properties of the studdied system represented in figure 1b), eg. an input PV power of around 70 W and an application power level of 5kW, result to a minimal value of the global power amplification factor PAFtot= 70. But in reality, when the sun radiation is poor, this factor can be much higher, and reach values of several hundreds. This was the main motivation of the realization of the two-stage system. The individual energetic properties of the components of the two stage system are represented in the diagram of figure 9. First the blue lines of the PV panels are drawn (one line per solar irradiance value), where the power should ideally be kept at the MPPT point corresponding to the unity value. The intersections with the black line of the Modified Ragone Representation of the supercapacitors show that the choice of these component is well adapted, and the MRR of the supercapacitors gives the value of the energy efficiency of this first energy transfer. The power level of the PV generator (P1 in figure 3) due to sunshine variations is represented as a variable power through the different blue curves in figure 9, it is comprized between 10 and 70 W. Then the energy transfer from the supercapacitors to the hydraulic accumulator is influenced as well by the MRR of the former component (the supercapacitors) for its discharge, as by the MRR of the hydraulic accumulator itself during its own charging. This energy transfer is represented through the green zone of figure 9, where one can see the optimal design due to simultaneous intersection of the curves at their respective maximums. The width of the green zone in figure 9 corresponds to the power variation of the charging impulses of the hydraulic accumulator due to the variation of its internal pressure related to its state of charge. Finally, the high power value of the final application (5kW) is represented by the vertical dotted red line. It can be read that the intersection with the MRR of the hydraulic accumulator corresponds to an acceptable energy exchange, the intersection point beeing in the region of the high performance of the bladder. One can easily see also that there is a total incompatibility between the curves of the PV panel and the final application, and also an incompatibility between the supercapacitive pre-storage and the same final application. The total power amplification factor of this two-stage application beeing equal to 5kW / 70W = 70 in the case of the highest PV power collected.

Practical realisation

Figure 10 illustrates the experimental verification equipment realized within the system-study and development. The system has been connected to a 100 Wp PV panel, and the output of the hydraulic accumulator has been connected to one hydraulic motor, itself coupled to a DC generator (according Fig. 3). The figure illustrates mainly the accumulation devices such as the supercapacitors (1) and the hydraulic accumulator (3), as well as motor-pump and control electronics.

Experimental results

The operation of the realized system is illustrated through the curves of figure 11. The successive rise and decrease of the pressure in the bladder illustrates the total cycle of the application (around 350s). The record includes also the value of the supercapacitor’s voltage Uscap, and the current Ipv provided by the PV panels. Within one total cycle of the charge and discharge of the second stage (the hydraulic accumulator), there are six “sub-cycles” of charge and discharge of the supercapacitors.

The slopes of the charge and discharge of the supercapacitors in figure 11 are of the same order of magnitude, illustrating the operation at high insolation of the PV panels. For an operation with low sun, the charging slope will be lowered. According the MRR of figure 9, a too low sunshine could lead to a poor efficiency if the intersections of the PV characteristics are situated at the left slope of the MMR diagram of the supercapacitors.

Conclusions

A two-stage power amplification equipment has been developed as an energy harvesting system for powering an application where the needed power level for the final application is not compatible with the available power of the small dimension PV collector. The first stage of the power amplification system has been realized with a bank of supercapcitors, particularly suited for the pre-storage of the low power delivered by the PV panels. The second stage is using a hydraulic accumulator, which can easily provide the high output power of the final application. The design of the equipment providing a power amplification factor higher than 70 has been done using the method of the MRR (Modified Ragone Representation), showing the good matching of the system components from the point of view of the partial and global energy efficiency. The input power levels of the global system are in the range of 10-70 W from the PV generator, while up to 5 kW are drawn from the final application.

  • Open access
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EXERGY-BASED OPTIMIZATION OF DISC-SHAPED HEAT EXCHANGERS
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Exergy

The continuous quest for improving the performance of heat exchangers, together with the evermore-stringent volume and weight constraints, especially in enclosed applications (engines, electronic devices), stimulates the search for compact, high-performance units. One of the shapes that emerged from a vast body of theoretical and applied research is the disc-shaped heat exchanger, in which the fluid to be heated/cooled flows through radial -often bifurcated- channels inside of a metallic disc. The disc in turn exchanges heat with the heat/cold source (the environment or another body).

Several studies have been devoted to the identification of an “optimal shape” of the channels: most of them are based on prime principles, but numerical simulations abound as well.

The present paper demonstrates that -for all engineering purposes- the correct design procedure for such a heat exchanger can be derived from a series of logical steps that follow necessarily (i.e., deterministically) from the technical specifications (exchanged thermal power, materials, surface quality): the design in fact reduces to a zero-degree of freedom problem.

The argument is described in detail, and it is shown that a proper application of the constraints completely identifies the shape, size and similarity indices of both the disc and the internal channels.

In a previous paper it was remarked that the goal of this kind of investigations is not that of “inventing” an unusual heat exchanger design procedure, but that of demonstrating that -in this as in many similar cases- a straightforward and diligent application of prime principles generates designs that completely satisfy the assigned specifications: in a practical sense, they enjoy a sort of “embedded” optimality.

The question arises, whether by including additional constraints in the design procedure (power density ratio, minimum volume, material and machining cost, life expectancy etc.) it is possible to refine the analysis and identify “optimal” configurations. The present study shows how a resource consumption indicator, the Exergy Footprint, can be calculated for different configurations and leads to (possibly non-unique) optimal designs.

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Closed Irreversible Cycles Design based on Finite Physical Dimensions Thermodynamics
Gheorghe Dumitrascu, Michel Feidt, Stefan Grigorean
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Fundamentals

Abstract: The paper develops generalizing entropic approaches of irreversible closed cycles. The mathematical models of the irreversible engines (basic, with internal regeneration of the heat, cogeneration units) and of the refrigeration cycles were applied to four possible operating irreversible trigeneration cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs unifying the first law of thermodynamics and the linear heat transfer law, the mean log temperature differences, and four possible operational constraints, i.e. constant heat input, constant power, constant energy efficiency and constant reference entropy. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input process. The number of internal irreversibility allows the evaluation of the heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The operational constraints allow the replacement of the reference entropy function of the finite physical dimensions parameters, i.e. mean log temperature differences, thermal conductance inventory, and the proper external heat reservoir temperatures. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration cycles. At the limit, i.e. endoreversibility, we can re-obtain the endoreversible energy efficiency equation. The second part develops the influences between the imposed operational constraint and the finite physical dimensions parameters for the basic irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratio of refrigeration rate to power, e.g. engine shaft power or useful power delivered directly to power consumers. The final disscusions and conclusions emphasize the novelties and the complexity of interconnected irreversible trigeneration systems design/optimization.

  • Open access
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Performance, Emissions and Durability Studies on Diesel Engine fuelled with a Preheated Raw Microalgal Oil
Hassan Attar, Dawei Wu, Adam Harvey
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Research and Development

More than 70% of the global trade is conducted by ships that consume fossil fuels, e.g. diesel oil (DO) and heavy fuel oil (HFO). International Maritime Organization (IMO) set forth regulations including MARPOL Annex VI in order to reduce total annual greenhouse gas emissions (GHG) from the global shipping, which can be achieved by using sustainable fuels, e.g. biofuels. Biofuels from microalgae are abundant in terms of its massive quantity of resources. Microalgae oil (MAO) has the potential to partially displace fossil fuels as a new marine fuel. MAO offers many benefits in the ecological and terrestrial preservation domain. This study examined the performance and emissions of a 4-stroke marine diesel engine fuelled with MAO from Schizochytrium sp. at variable speed and load. The experimental results were compared with DO in terms of brake power, torque, brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), brake mean effective pressure (BMEP), heat release rate (HRR), in-cylinder pressure, NOx and CO emissions. Also, an engine durability test for its longevity was investigated when the engine fueled with raw MAO. The research reveals the potential of raw MAO as a supplement marine fuel to non-renewable fossil fuels, which may assist in achieving the emissions reduction targets set by IMO.

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GREEN PERSPECTIVES FOR DEPLETED OIL & GAS WELLS IN ITALY
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Conversion Systems

The decarbonisation of the energy sector is probably one of the main worldwide challenges of the future. Global changes urge a radical transformation and improvement of the energy producing systems to meet the decarbonisation targets of the European economy by 2050 and a reduction of greenhouse gas emissions. Also the hydrocarbon industry contributes to this transition path: since ’90, American and Chinese oil companies have studied the possibility of use the waste heat produced from oil and gas wells. As a matter of fact, the mature stage of oil and gas fields is often characterized by the production of hydrocarbons and formation waters, which must be treated continuously and reinjected in the reservoir. The volume of produced water increases with the maturity of the assets, so when the hydrocarbons wells are going to be depleted, the conversion into geothermal wells could be an alternative to the mining closure. In the described transition scenario, the geothermal energy seems very promising because it is characterized by a wide range of applications and uses depending by the temperature of extracted water. This flexibility enables to propose projects inspired to circular economy vision, sustainability, integration in the territory and social acceptance. In Italy, since 1985, 7246 well have been drilled for hydrocarbon. According to the last update provided by the Italian Ministry for Economic Development, there are 2166 active wells in Italy of which 1434 are located onshore in the existing mining licenses. The paper presents a preliminary investigation on some oil and gas wells located on Italian territory based on the available information provided by the Ministry of Economic Development. Then, taking into account the activities or land use of the territory, a conversion strategy for the producing wells has been proposed for three case studies: Irminio, Gaggiano and Villafortuna-Trecate.

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Reducing the cooling energy consumption of telecom sites by liquid cooling
Jari Huttunen, Eva Pongrácz, Olli Salmela
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Conversion Systems

The use of mobile data has increased and will continue to increase in the future due to new radio technologies, such as 5G. Despite improvements in the energy efficiency of the telecommunications equipment, the total energy consumption telecommunication is rising due to increased data traffic. In addition to the equipment’s own energy consumption, there is also the energy need of site cooling when using indoor telecom rooms. Currently, all the equipment are air-cooled and sites are either ventilated or air conditioned. The power consumption of site cooling can even be as high as the equipment’s own power consumption.

In this paper, we discuss the world’s first liquid Base Transceiver Station (BTS) that was taken into commercial use in 2018, in Helsinki, Finland. Conventional air-cooled BTS HW was converted into liquid-cooled BTS, by removing the fans and replacing the heat sinks by matching cold plates. Heat from the BTS was pumped out of the site room and thus ventilation or air conditioning was not needed for the heat load from the BTS. It is also possible to reuse the thermal energy stored in the liquid for heating the building or the utility water.

As an interim solution, heat stored in the liquid was released into the ventilation duct of the building, still providing annual cooling energy savings of 93%, when compared to air-cooling. In the future, 80% of the total dissipated energy, 15900kWh/a in total, can potentially be used for heating purposes. Additional benefits include reduced CO2 emissions and operational costs. In terms of CO2 emissions, adapting liquid cooling showed an 80 % reduction potential when compared to air-cooling.

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  • 15 Reads
Investigation on the lean stable limit of a Barrier Discharge Igniter and of a Streamer-type Corona Igniter at different engine loads in a single-cylinder research engine.
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Conversion Systems

Currently, the Radio-Frequency Corona Ignition systems represent an important solution for reducing pollutant emissions and fuel consumption related to Internal Combustion Engines while at the same time ensuring high thermal efficiency and performance.

These igniters are able to extend the lean stable limit by increasing the early flame growth speed. Kinetic, thermal and ionic effects, together with the particular configuration of the devices, allow to start the combustion process in a wider region than the one involved by the traditional spark.

In this work two corona igniters, namely a Barrier Discharge Igniter and a Corona Streamer Igniter, were tested in a single-cylinder research engine fueled with gasoline at different engine loads in order to investigate the igniters performance through the indicated analysis and pollutant emissions analysis.

For each operating point, maximum level of activation time and driving voltage have been used for both the igniters with the aim of investigating, at the extreme operating conditions, the capability of the devices to extend the lean stable limit of the engine.

The Corona igniters have been tested on a constant volume calorimeter as well, reproducing the engine pressure conditions at the corresponding ignition timing. The target is to give an estimation of the thermal energy released during the discharge and then to compare their capability to provide high-stability energy.

  • Open access
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Sustainable energy solutions for rural communities
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Policy

This paper summarizes the experiences of the RECENT project, which intended to enhance the utilization of unused assets in remote and sparsely populated areas and communities. The project’s objectives were to enhance energy efficiency, implement renewable energy solutions and help communities to have more resilient and energy efficient public infrastructures capable of handling climate change related risks. The project developed 25 pilots related to energy, energy efficiency, waste, and water solutions across five Northern Periphery and Arctic Programme (NPA) partner regions (Finland, Sweden, Northern Ireland, Ireland, and Scotland).

The project assessed the energy generation and/or reduction potential of pilots; investment costs and payback times were also calculated. In addition, a sustainability assessment tool was developed, in order to assess the environmental, social and long-term sustainability of the pilots to evaluate the progress of communities toward sustainability.

The paper will present selected pilots across the five regions, including their energy generation and/or saving potential and investment and payback time, as well results of their sustainability. The combined benefit of the 25 pilots is 20 GWh/year renewable energy and saving 6,070 t of CO2/year. In addition, the sustainability assessment also highlighted the social benefits to the community.

The project established the opportunity for a new way of providing environmental goods and services and to support innovative infrastructures based on the integrated management of resources, such as water, waste and energy with land-use decisions, and efforts of preservation of biodiversity. These integrated infrastructures would be based on decentralized systems which allow for synergies between different systems. In turn, these synergistic solutions can contribute significantly to the reduction of resource consumption and related emissions as well as to the sustainable development of European communities.

  • Open access
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Solar thermal technologies for low-carbon industrial processes: dynamic modelling, techno-economic analysis and environmental impact.
Michele Bolognese, Luigi Crema, Luca Pratticò, Diego Viesi, Ruben Bartali
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Energy Conversion Systems

Fossil fuels, playing a dominant role in the worldwide energy system, negatively contribute to the environment and the climate. In order to limit global warming to well below 2°C, rapid and deep decarbonisation of industrial processes is required. Solar thermal technologies are already available in the market, robust and relatively cheap. Unfortunately, the solar heat is little used in the industrial processes. The main obstacles of the solar heat diffusion is often the lack of an adequate predictive modelling of solar plant integration, identifying its energy potential, economic feasibility and environmental benefits. In this paper, the case study of a pasta factory called "Felicetti", located in the north-east of the Italian Alps, has been considered in order to investigate and evaluate the possibility of supplying solar heat for the pasta drying process. The methodology proposed is structured in several steps: (I) industrial process characterization; (II) collection of local hourly data for radiation and climatic temperature; (III) study of the position of sun and components of incident angle; (IV) comparison among three solar technologies (Compound Parabolic Collectors, Linear Fresnel Reflectors, Parabolic Trough Collectors), in terms of overall efficiency and heat production; (V) focus on Parabolic Trough Collectors: characterization of fluid dynamics parameters and heat exchanger design; (VI) dynamic modelling with Dymola – Dassault Systems ® (heat thermal fluid temperature, solar heat production, solar fraction); (VII) study of economic and environmental impact. The dynamic modelling results show that the integration of Parabolic Trough Collectors in the available surfaces of the Felicetti Pasta Factory can guarantee a solar fraction of 23% in a typical week of June saving about 4.7 tCO2/week. The economic analysis shows a pay-back time up to 9 years and a reduction of CO2 emissions up to 99 t/year. The methodology developed is tested combining solar energy with different energy sources, including 100% renewable solutions, in different geographical contexts. Moreover, it can be replicated on a wide range of industrial processes.

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  • 7 Reads
Selecting the optimal use of the geothermal energy produced with a deep borehole heat exchanger: energy vs exergy performance
Published: 11 September 2020 by MDPI AG in The First World Energies Forum session Exergy

The decarbonization of the energy sector is probably one of the main worldwide challenges of the future. Global changes urge a radical transformation of the energy producing systems to meet the 2050 EU targets. In this context, the geothermal sector has a strength point respect to other renewable energy sources: the availability of a wide range of applications depending by the temperature of extracted resource.

Since 2000, several researches have been focused on the possibility to produce geothermal energy without brine extraction. This solution entails the use of a deep borehole heat exchanger, composed by an external steel casing and two internal coaxial tubes, also in steel. The internal tubes are separated by an insulation, necessary to avoid heat exchange between the downward fluid and the upward one. The coaxial heat exchanger acquires heat by conduction with the external ground and transfers the heat via conduction and convection to a working fluid which circulates in the device. The possibility of produce geothermal energy with a zero-mass extraction device may be the key to increase the social acceptance, to reduce environmental impact of geothermal projects. and to exploit the unconventional geothermal systems, where the extraction of brines in technically complex.

The exergy, also called available work, is a measure of the maximum work output that could theoretically be obtained from any system interacting with a given environment which is at constant pressure and temperature. The exergy also represents the minimum work needed by a thermal machine based on the reverse cycle, such as heat pumps and chillers. The exergy analysis evaluates the irreversible production of entropy; therefore, it is useful to identify both the maximum theoretical performances and the inefficiencies of a system and its components. Besides, it represents a coherent quantity to compare energy systems with different energy outputs, such as electricity and heat at different temperatures.

In this work the exergy efficiency has been used as evaluation criteria to select the best utilization strategy of the heat produced by means of a deep borehole heat exchanger. Five configurations have been proposed and analyzed: a district heating plant, a absorption cooling plant, an ORC plant to produce electricity, a cascade system composed by district heat and cooling, a cascade system composed by the ORC plant and DH plant. A sensitivity analysis has been conducted using the BHE simulator named GEOPIPE and changing the utilization temperatures of thermal utilities, the main parameters affecting the operation of the borehole heat exchanger, and the temperature of the geothermal source.

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